1. Field of the Invention
The invention is in the field of crystal growth.
2. Brief Description of the Prior Art
Many crystalline materials of commercial and scientific interest can be produced by the mixture of two solutions if a suitable technique can be found to avoid the problems inherent in such a process. Such processes depend upon the mixture of solutions producing a supersaturation of the desired product in the mixed solution. One important phenomenon to be avoided is the spontaneous nucleation of tiny crystals throughout the solution and immediate precipitation.
In order to accomplish the growth of usefully large crystals several techniques have been developed, generally involving slow introduction of one solution into the other or of both into a third substance. One of these techniques involves the growth of crystals in a gel (Crystal Growth in Gels, H. K. Henisch, Pennsylvania State University Press, 1970). These methods variously involve incorporation of one solution in a gel and diffusion of material from a contacting liquid into the gel, producing supersaturation and crystal growth within the gel, or diffusion of two solutions contacting opposite sides of a gel containing a third liquid. Other methods involve the slow introduction of two solutions into a third liquid by, for example, slowly dripping the solutions into a body of the third liquid or diffusion of material from the two solutions through semipermeable membranes into the third liquid (The Growth of Single Crystals, R. A. Laudise, Prentice-Hall, 1970, page 271) or by introduction of the two solutions through two gel plugs into the third body of liquid (Journal of Crystal Growth, Vol. 12 1972, page 179).
In the above-mentioned methods the nature of the gels and semipermeable membranes used, places restrictions on the chemical systems to which these methods can be applied. That is to say: The material of the gel is sometimes incorporated in the crystal as a contaminant; the structure of the gel is in many cases sensitive to solution parameters, such as pH; the rate of diffusion of materials through gels is difficult to vary over wide ranges; and semipermeable membranes of the desired selectivity are not always available.